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Abstract

Laser emission over a broad range of frequencies from 2.8 to 4.1 THz is reported for a two-quantum well, photon-phonon cascade structure. Maximum operating temperatures of 125 K are reported, with optical peak powers in eccess of 30 mW from a double-metal ridge waveguide. The broadband nature of the gain curve is identified as due to coherent coupling of the injector and upper lasing states. Internal quantum efficiencies reaching 43 % are evaluated at 10 K. The laser operates in both polarities, showing laser action in reverse bias up to a temperature of 90 K. Simulations based on a full treatment of the structure with density matrix formalism are also presented and discussed.

Figures (6)

Calculated bandstructure for two periods of sample EV1183 for an applied electric field of 14 kV/cm. The layer sequence is (nm, starting with the injection barrier): 4.5/8.3/3.8/17.9. The figures in bold face represent the Al0.15Ga0.85As barriers. The central part of the 17.9 nm GaAs well is doped in order to obtain a sheet carrier density of 1.5 × 1010cm-2, measured with C-V technique. The location of the doping in the well is chosen to minimize the overlap of the state ∣2〉 wavefunction with the doped region.

Pulsed measurements in direct bias as a function of heatsink temperature for a 1.36 mm long, 180 μm wide double metal laser ridge with the top partially covered with metal, as schematized in the inset. The ridge width is taken as the width of the metal. The power has been measured with a broad area, calibrated THz power meter.

(a): Continuous wave measurements and differential analysis for a laser ridge (red) and a non-lasing device (blue ) at T=10 K. The arrows highlight the electric field values corresponding to the resonance features. The region between the dashed lines is the fraction of radiative current due stimulated emission. (b): Simulation of the gain curve for a lasing device for an electric field of 12.5 kV/cm for a lattice temperature T=50 K. (c): Simulated transport curves in delocalized basis (black curve), tight-binding basis (blue curve) for a lasing device and in tight binding basis for a non-lasing device (light-blue, dashed curve), all for a lattice temperature T=50 K. The red curve is an experimental, CW curve for a lasing device. The green curve is a simulation of the emitted laser signal.

(a): Pulsed measurements in reverse bias for a standard double metal laser ridge of 1.7 mm length and 160 μm wide. The detector used is an He-cooled Si-bolometer. (b): Complete spectral emission in pulsed mode at T=10K for both direct (red curves) and reverse (black curves) bias as a function of the injected current density.